1. Field of the Invention
The present invention relates to a braun tube reproducing a received electric signal as a video signal, and in particular to a deflection yoke for a braun tube which is capable of deflecting an electron beam radiated from an electron gun toward a screen.
2. Description of the Prior Art
A braun tube is for displaying a picture by converting an electric signal into an optical image such as a graphic, a character, etc. by an operation of an electron beam and is used for a video display unit such as a television, a monitor, etc.
As depicted in FIG. 1, a braun tube includes a funnel 10 as a vacuum bulb, a panel 12 maintaining a vacuum state by combining with the funnel 10 and reproducing colors by a R.G.B (Red, Green, Blue) fluorescent substance coated at its inner surface, an electron gun 14 installed at the rear of the funnel 10 and radiating R.G.B electron beams toward the panel 12, a shadow mask 16 installed with a certain distance from the panel 12 and performing a color selection function, and a deflection yoke 20 installed at a neck portion 11 of the funnel 10 and deflecting an electron beam radiated from the electron gun 14.
Herein, the deflection yoke 20 deflects an electron beam radiated from the electron gun 14 by using the principle of a magnetic field generated by a coil in order to make the electron beam sequentially contact to a pertinent pixel on a request position of a screen 12a. 
The deflection yoke 20 includes a horizontal deflection yoke 21 deflecting an electron beam in a horizontal direction on the basis of a center of deflection by generating a magnetic field in a vertical direction, a vertical deflection coil 23 deflecting an electron beam in a vertical direction on the basis of the center of deflection by generating a magnetic field in a horizontal direction, and a ferrite core 25 preventing a magnetic field generated by currents applied to the horizontal and vertical deflection coils 21, 23 from leaking out and strengthening a magnetic force at the same time.
And, the deflection yoke 20 includes a holder 27 determining correlation positions of the horizontal deflection coil 21 and vertical deflection coil 23, and guaranteeing insulation between them.
In the braun tube in accordance with the prior art, when an electron beam is radiated from the electron gun 14, the electron beam reaches to the screen 12a through the deflection yoke 20, herein the electron beam moves in a horizontal direction under the influence of a magnetic field of the horizontal deflection coil 21 and in a vertical direction under the influence of a magnetic field of the vertical deflection coil 23.
Accordingly, the electron beam radiated from the electron gun 14 can reach to the whole parts of the screen 12a by motions in both the horizontal and vertical directions under the influence of the horizontal and vertical deflection coils 21, 23.
And, the ferrite core 25 is for forming the deflection force sufficiently by preventing the magnetic field generated by the vertical and horizontal deflection coils 21, 23 from leaking out to a surrounding space and strengthening the magnetic force at the same time.
However, in the braun tube in accordance with the prior art, because the deflection yoke 20 is installed outside of the funnel 10, it is easy to adjust a position of the deflection yoke 20, accordingly the convergence and deflection sensitivity of an electron beam can be easily compensated. However, the deflection performance may lower due to expansion of the magnetic field from the center of the deflection. And, because the deflection yoke 20 is externally exposed, the deflection yoke 20 may be physically affected in the manufacturing process or delivery and has to be reset in that case.
Accordingly, in order to solve problems of the braun tube including the deflection yoke 20 installed outside of the funnel 10, an in-neck deflection yoke type braun tube including the deflection yoke 20 which is installed inside the funnel 10 has been developed.
As depicted in FIG. 2, in an in-neck deflection yoke type braun tube, a deflection yoke 20xe2x80x2 is installed inside a funnel 10xe2x80x2.
In other words, a holder 27xe2x80x2 attached to an electron gun 14xe2x80x2 is installed inside the funnel 10xe2x80x2, the holder 27xe2x80x2 is constructed so as to support a horizontal deflection coil 21xe2x80x2, a vertical deflection coil 23xe2x80x2 and a ferrite core 25xe2x80x2.
As described above, when the deflection yoke 20xe2x80x2 is installed inside the funnel 10xe2x80x2, a neck portion 11xe2x80x2 of the funnel 10xe2x80x2 is wider than the neck portion 11 of the braun tube of FIG. 1, and the overall outer structure of the braun tube can be simplified.
Particularly, the in-neck deflection yoke type braun tube can have the more improved deflection sensitivity on the comparison with the braun tube of FIG. 1 as the deflection yoke 20 is installed outside of the funnel 10, the reason will now be described.
In general, the deflection sensitivity of an electron beam can be described as power generated by currents and voltages applied to deflection coils performing deflection in the vertical and horizontal directions, it can be described as below.                               P          H                =                              1            2                    ⁢                      L            H                    ⁢                      I            H            2                                              (        1        )                                          P          V                =                              1            2                    ⁢                      R            V                    ⁢                      I            V            2                                              (        2        )            
Herein, PH and PV describe the horizontal deflection sensitivity and vertical deflection sensitivity, respectably, LH and RV describe the inductance of a horizontal deflection coil and the resistance a vertical deflection coil, respectively, and IH and IV describe currents applied to the horizontal deflection coil and vertical deflection coil, respectively.
With reference to the above-described equations 1 and 2, it is better to improve the deflection sensitivity of the braun tube with a small quantity of power, accordingly the more PH and PV lower in equations 1 and 2, the more the deflection sensitivity improves.
In a general braun tube, when a frequency of current applied in a horizontal direction is a high frequency not less than 15.75 kHz, an inductance value is a main adjustment factor, on the contrary when a frequency of current applied in a vertical direction is a low frequency as 60 Hz, a resistance value is a main adjustment factor.
Accordingly, in order to improve the deflection sensitivity of the braun tube, a LH value of the horizontal deflection coil and a RV value of the vertical deflection coil have to lower on the basis of the same current value.
Accordingly, in the in-neck deflection yoke type braun tube, because the deflection yoke 20xe2x80x2 is installed inside the funnel 10xe2x80x2, although the same amount of current is applied to the horizontal and vertical deflection coils 21xe2x80x2, 23xe2x80x2, the deflection force of an electron beam in up-and-down and right-and-left directions can improve by generating a bigger magnetic field inside the funnel 10xe2x80x2.
In the in-neck deflection yoke type braun tube, because the deflection yoke 20xe2x80x2 is installed inside the funnel 10xe2x80x2, external physical influence can be minimized. However it is difficult to compensate the convergence and deflection sensitivity of an electron beam after the deflection yoke 20xe2x80x2 is installed.
In addition, in the in-neck deflection yoke type braun tube, gas elements included in the ferrite core 25xe2x80x2 of the deflection yoke 20xe2x80x2 can leak inside the funnel 10xe2x80x2 due to a high temperature circumstances in the fabrication process of the braun tube or operation of the braun tube, it may damage a characteristic of the braun tube which can show the sufficient performance in a vacuum state, accordingly lots of work are required in order to prevent it.
In order to solve above-mentioned problems, an object of the present invention is to provide a deflection yoke for a braun tube which is capable of compensating the convergence and deflection sensitivity of an electron beam, and increasing the degree of freedom in designing a deflection yoke and an electron gun required for enlarging a diameter of an electron gun by installing a ferrite core outside of a funnel and installing a horizontal deflection coil and a vertical deflection coil inside the funnel.
In order to achieve the object of the present invention, there is provided a deflection yoke for a braun tube in accordance with embodiments of the present invention installed at a neck portion of a funnel and including a horizontal deflection coil, a vertical deflection coil and a ferrite core in order to deflect an electron beam radiated from an electron gun toward a determined position of a screen, the vertical deflection coil is installed inside a funnel, the ferrite core is installed outside of the funnel, and the vertical deflection coil is installed inside or outside of the funnel.
In an embodiment of the present invention, a vertical deflection coil is installed inside a funnel and is fixed by a first holder attached to an electron gun with a horizontal deflection coil. And, a ferrite core is fixed to outside of the funnel by a fixing means and its inner diameter is larger than an outer diameter of the funnel so as to move in up-and-down and right-and-left directions outside of the funnel.
In another embodiment of the present invention, a vertical deflection coil is installed outside of a funnel with a ferrite core.